a-glass? If so, you
know you must make the tube longer or shorter according as you look at
things near by or far away. The eye also has to be changed a little
when we look from near to distant objects. Look out of the window at a
tree a long way off. Now place a lead pencil between the eyes and the
tree. You can scarcely see the pencil while you look sharply at the
tree, and if you look at the pencil you cannot see the tree distinctly.

~22.~ There is a little muscle in the eye which makes the change needed
to enable us to see objects close by as well as those which are farther
away. When people grow old the little muscles cannot do this so well,
and hence old people have to put on glasses to see objects near by, as
in reading. Children should not try to wear old persons' glasses, as
this is likely to injure their eyes.

~23. How to Keep the Eyes Healthy.~--(1.) Never continue the use of the
eyes at fine work, such as reading or fancy-work, after they have become
very tired.

(2.) Do not try to read or to use the eyes with a poor light--in the
twilight, for instance, before the gas or lamps are lighted.

(3.) In reading or studying, do not sit with the light from either a
lamp or a window shining directly upon the face. Have the light come
from behind and shine over the left shoulder if possible.

(4.) Never expose the eyes to a sudden, bright light by looking at the
sun or at a lamp on first awaking in the morning, or by passing quickly
from a dark room into a lighted one.

(5.) Do not read when lying down, or when riding on a street car or
railway train.

(6.) If any object gets into the eye have it removed as soon as
possible.

(7.) A great many persons hurt their eyes by using various kinds of
eye-washes. Never use anything of this kind unless told to do so by a
good physician.

~24. How we Smell.~--If we wish to smell anything very strongly, we
sniff or suddenly draw the air up through the nose. We do this to bring
more air to the nerves of smell, which are placed at the upper part of
the inside of the nose.

[Illustration: INSIDE OF THE NOSE.]

~25.~ Smelling is a sort of feeling. The nerves of smell are so
sensitive that they can discover things in the air which we cannot taste
or see. An Indian uses his sense of smell to tell him whether things
are good to eat or not. He knows that things which have a pleasant smell
are likely to be good for him and not likely to make him sick.

We do not make so